Here are some example medical device patents that employ ball joints: 3,017,887 and application 20030040753. They both have adjustable friction on the ball. You can get copies here: http://www.pat2pdf.org/
I have a design where a magnet will be sliding on a magnetic surface (only need a life of ~10 cycles of magnet sliding on surface). I've selected a rare earth magnet that has a polished surface. Per the tips here I'm going with thin, annealed 1018 CRS for the magnetic plate. I need a corrosion...
